The decision blocks the law designed to prevent therapists from trying to change minors' sexual orientation pending a ruling on its constitutionality.

A federal appeals court Friday put a hold on a new state law intended to prevent therapists from trying to change a minor's sexual orientation, dealing a setback to gay rights groups.

A three-judge panel of the U.S. 9th Circuit Court of Appeals agreed to block the law, scheduled to take effect Jan. 1, pending a decision on its constitutionality.

"This is a very good sign for our clients," said Mathew Staver, found of Liberty Counsel, a religious liberties group that sued to block the law, arguing that it violates free speech rights. "To get an injunction pending appeal is a very difficult thing to do."

A spokeswoman for state Atty. Gen. Kamala D. Harris said Harris would "vigorously defend" a law that banned what she termed an "unsound and harmful practice."

The law would subject psychologists, psychiatrists and other mental health professionals to discipline by their licensing boards for providing minors therapy to change their sexual orientation. The state and many professional groups say the therapy is ineffective and potentially dangerous.

A District Court judge initially rejected the suit by Liberty Counsel, whose clients include a 15-year-old boy undergoing the therapy. The Christian-oriented legal group appealed that decision to the 9th Circuit.

The judges who are hearing the case are Alfred T. Goodwin, appointed by President Nixon; Edward Leavy, a Reagan appointee; and Milan D. Smith Jr., named to the court by President George W. Bush.

Staver, calling the preliminary injunction "very welcome news," said it was "never routine" and granted only in extraordinary situations when the court believes an appeal has a "likelihood of success."

UC Irvine Law School Dean Erwin Chemerinsky, who believes that the law is constitutional, said its opponents "won this round."

"This doesn't determine the ultimate outcome by the 9th Circuit," the constitutional law expert said. "It still has to rule on the merits, and it could well go to the Supreme Court. But obviously this is a preliminary loss for supporters of the law."

California's ban on trying to change a minor's sexual orientation, the first of its kind in the nation, has divided the lower courts. The federal judge in Sacramento who refused to block the law was appointed by President Obama. She concluded that it did not violate the 1st Amendment. Her colleague on the same bench, appointed by President George H.W. Bush, concluded that it was likely that the law infringed on free speech protections.

Communication between professionals and their clients generally has less 1st Amendment protection than other forms of speech. For instance, a lawyer or doctor who negligently gives bad advice may be found liable for malpractice, and licensing requirements for professionals may be restrictive.

The Supreme Court upheld a law that required doctors to tell patients about potential harmful effects of an abortion, but the 9th Circuit blocked a federal law designed to prevent doctors from discussing the benefits of marijuana with patients.

A task force report by the American Psychological Assn. in 2009 said the therapy could trigger depression, suicide and substance abuse, but also noted that there was scant research on the issue.

The new law was supported by the California Psychological Assn., the California chapter of the National Assn. of Social Workers and the California Division of the American Assn. for Marriage and Family Therapy.

Gay rights activists Friday minimized the setback and noted that the court has agreed to review the law on a fast track.

"Every leading medical and mental health organization has warned therapists and parents that these practices do not work and put young people at risk of serious harm, including depression and suicide," said Shannon Minter, legal director of the National Center for Lesbian Rights. "No young person should be subjected to these dangerous practices, and no licensed therapist should be permitted to engage in practices that cause such serious harm."